I haven't tried this but that's what it says on the Chinese FAQ which some of the above FAQ is based on.

I had TTS right after installation. It worked with the dictionary also, with the default female and male voices. I then installed the aforementioned WyabdcRealPeopleTTS in system/dict. All this gives you is a nice female voice for the dictionary. It does nothing for the book TTS. It is a whopping 166mb folder (my poor Kindle was glowing and giving off smoke as I copied it over, and I heard the terrified voices of the 300 books that it displaced!).

All in all, not very important unless you like your dictionary to read to you.

Would there be a way to install this for the book TTS? Somehow, I doubt it.